The rail surface of railway tracks experiences wear due to wheel-rail interactions. Over time, the rail surface may often exhibit defects known as corrugation, which is a form of cyclical wear. Severe corrugation will reduce the service life of rail vehicles that run on the rail, meaning that is important for railway and infrastructure operators to be able to detect such surface defects so that necessary track maintenance can be performed.
Track recording vehicles are known, which include instruments for measuring many different attributes of a railway track. These are specialized vehicles which can be operated only at infrequent intervals, especially on busy lines. The use of in-service vehicles is much preferable.
One example of a method for detecting rail-top defects using measurements obtained from sensors that can be mounted to an in-service vehicle is known from EP 2464555. The method employs an axle box acceleration signal. A vertical and a longitudinal axle box acceleration signal are measured, whereby the longitudinal acceleration is used to remove a signal part from the vertical acceleration signal that relates to vibrations of the wheel set.
A further example is disclosed in U.S. Pat. No. 6,668,239. The method is carried out using a vehicle that is equipped with a vertical acceleration sensor mounted to the vehicle frame at each side of the bogie. The instrumentation package further includes a linear displacement transducer connected between the frame a wheel bearing at each axle end, for measuring vertical displacements of the wheel relative to the frame. The acceleration signal is digitized and subjected to double integration, to obtain vertical displacements of the frame. The corresponding displacements of the top surface of the rail are calculated from the obtained vertical frame displacements and the measured displacements of the wheel relative to the frame.
There is room for improvement.